<template>
	<ul class="list">
		<li 
			class="item" 
			v-for="item of letters" 
			:key="item" 
			:ref='item'
			@click="handleLetterClick" 
			@touchstart="handleTouchStart"
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
		>{{item}}</li>
	</ul>
</template>

<script>
	export default{
		name: 'CityHeader',
		props: {
			cities: Object
		},
		computed: {
			letters() {
				const letters = []
				for(let i in this.cities) {
					letters.push(i)
				}
				return letters
			}
		},
		data() {			//标时位
			return {
				touchStatus: false,
				startY: 0,
				timer: null
			}
		},	
		updated () {
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods: {
			handleLetterClick (e) {
				
				this.$emit('change', e.target.innerText)
			},
			handleTouchStart () {
				this.touchStatus = true
			},
			handleTouchMove (e) {
				if (this.touchStatus) {
					if (this.timer) {
						clearTimeout(this.timer)
					}
					this.timer = setTimeout(() =>{
						const touchY = e.touches[0].clientY -93
						const index = Math.floor((touchY - this.startY)/20)
						if (index >= 0 && index < this.letters.length){
							this.$emit('change', this.letters[index])
						}
					}, 16)
					//const startY = this.$refs['A'][0].offsetTop
					//console.log(startY)
					
					
					
				}
			},
			handleTouchEnd() {
				this.touchStatus = false
			}
		}
	}
	
</script>
<style scoped>
	.list{
		position: absolute;
		top: 1.58rem;
		right: 0;
		 bottom: 0;
		 width: .4rem;
		 
		 display: flex;
		 flex-direction: column;
		 justify-content: center;
	}
	.item{
		text-align: center;
		line-height: .44rem;
		color:#00BCD4;
		list-style-type:none;
	}
</style>